(1) Field of the Invention
The present invention relates to benzylated lignocellulosic substances and a producing method thereof, and more particularly to benzylated lignocellulosic substances suited for use as material to be foamed for producing foamed molded articles without adding a plasticizer and a producing method thereof.
(2) Description of the Prior Art
The recent growth of the petrochemical industry has brought about the production of various kinds of plastics and our life is so closely related to products made from plastics that life without plastics is no longer imaginable. However, since plastics produced in the petrochemical industry are not biodegraded by microorganisms in nature, there have been increasingly accumulated used plastics and now vast amounts of plastic waste cause serious pollution problems.
One of the attempts which have been made to solve the above problem is that used plastic products are collected and decomposed in chemical reactors for recycling. However, the practical use of such recycling is thought to be difficult for the following reasons. First, the cost of the collection is higher than the manufacturing cost of plastic products. Another reason is that, since high temperature is generated in burning plastics and injurious ingredients are discharged when burning plastics in a reactor, the reactor is tremendously harmed, leading to the increased running cost of the equipment. In these circumstances, there have been a pressing need for the development of substances which can replace plastics manufactured in the petrochemical industry. Such substances should be easily molded and should posses physical properties (e.g., strength) to withstand practical use, as well as biodegradability.
Wood is a typical, natural, high molecular lignocellulosic substance, which contains cellulose, hemicellulose and lignin as main components. Such high molecular lignocellulosic substances do not have thermoplasticity in themselves so that it is thought to be impossible to mold high molecular lignocellulosic substances into various shapes like plastics manufactured in the petrochemical industry.
Nobuo Shiraishi, who is one of the inventors of the present invention, has found that thermal flowability can be imparted to etherificated or esterificated wood flour by hot pressing and he has introduced, in the past, etherificated wood flour and esterificated wood flour as lignocellulosic substances having plasticity. In general, lignocellulosic substances having plasticity are more brittle than plastics manufactured in the petrochemical industry and inferior to the latter in physical properties such as strength. Of lignocellulosic substances having plasticity, etherificated lignocellulosic substances have comparatively high softening points and suitable physical properties. Of etherificated lignocellulosic substances, particularly benzylated lignocellulosic substances exhibit high softening points and suitable physical properties. Further, the voluminous spatial configuration of benzyl groups in benzylated lignocellulosic substances acts as steric hindrance, reducing the degree of the substitution of hydroxyl groups in, for example, a glucose residue contained in wood. Chemical properties, which reduce the degree of substitution, allow hydroxyl groups to remain in the substances, and thanks to the remaining hydroxyl groups, biodegradation takes place in nature.